Radiocarbon analysis in an Alpine ice core: record of anthropogenic and biogenic contributions to carbonaceous aerosols in the past (1650–1940)

摘要

Long-term concentration records of carbonaceous particles (CP) are ofincreasing interest in climate research due to their not yet completelyunderstood effects on climate. Nevertheless, only poor data on theirconcentrations and sources before the 20th century are available. Wepresent a first long-term record of organic carbon (OC) and elemental carbon(EC) concentrations – the two main fractions of CP – along with thecorresponding fraction of modern carbon (f_M) derived from radiocarbon(14C) analysis in ice. This allows a distinction and quantification ofnatural (biogenic) and anthropogenic (fossil) sources in the past. CP wereextracted from an ice archive, with resulting carbon quantities in themicrogram range. Analysis of 14C by accelerator mass spectrometry (AMS)was therefore highly demanding. We analysed 33 samples of 0.4 to 1 kg icefrom a 150.5 m long ice core retrieved at Fiescherhorn glacier in December2002 (46°33'3.2" N, 08°04'0.4" E; 3900 m a.s.l.). Samples were takenfrom bedrock up to the firn/ice transition, covering the time period1650–1940 and thus the transition from the pre-industrial to the industrialera. Before ~1850, OC was approaching a purely biogenic origin with amean concentration of 24 μg kg−1 and a standard deviation of 7 μg kg−1.In 1940, OC concentration was about a factor of 3 higherthan this biogenic background, almost half of it originating fromanthropogenic sources, i.e. from combustion of fossil fuels. The biogenic ECconcentration was nearly constant over the examined time period with 6 μg kg−1and a standard deviation of 1 μg kg−1. In 1940, theadditional anthropogenic input of atmospheric EC was about 50 μg kg−1.